This application is related to co-pending application Ser. No. 318,301, filed Nov. 5, 1981, entitled REDUCED MAINTENANCE EXPLOSION DAMAGE RESISTANT STORAGE BATTERY.
This application relates to the field of storage batteries. In particular, this application relates to structure integral with a storage battery rendering it explosion damage resistant, and providing gas recombination means to reduce or eliminate the need for maintenance in the form of water addition.
Conventional lead-acid storage batteries, such as used for heavy duty charge-discharge applications, including such uses as powering industrial trucks, industrial street vehicles and mine locomotives, require frequent replacement of water. Water is lost from such batteries due to the electrolysis of the water in the electrolyte into hydrogen and oxygen, as well as through evaporation. This electrolysis occurs to a slight extent during operation of the battery, but primarily during overcharge, when at least some cells of the battery have accepted substantially full charge, and additional energy supplied is expended in electrolysis.
This problem is particularly severe when batteries are built for extended life, by the addition of antimony to the lead grids to increase the tensile strength and retard the degradation of the positive active material. This addition also causes undesirable side effects, which increase the internal losses of the battery, resulting in a decrease in overall battery efficiency, and an increased need for water additions. This problem has largely been overcome by substituting calcium as the hardening agent for the grids, resulting in a reduced amount of required overcharge.
The gases evolved from a battery, primarily oxygen and hydrogen, combine explosively when ignited. If ignited external to the battery, the flame enters the volume of gas confined within the battery, causing an explosion of the battery. There have been numerous attempts to solve this problem by keeping the advancing flame front from entering the battery by the use of porous membranes, which cool the gases below their ignition temperature. However, in industrial applications, it may occur that a severe overload may cause a portion of the internal structure of the battery to melt explosively, in turn igniting the gas within the battery, and causing the battery to explode. Since the source of ignition is internal to the battery, devices which cool a flame front advancing towards the battery are of no effect.
Batteries may also be provided with catalytic recombination devices containing platinum or palladium, to recombine the oxygen and hydrogen generated by the disassociation of water during the overcharge. Such devices are well-known and readily available in the form of replacement vent caps, which fit onto the top of the battery. Unfortunately, such units require considerable extra space over the top of the battery and, in most cases, this additional height is not available. In batteries for electric industrial trucks, the height of the cell is at a maximum, in order to provide the maximum number of kilowatt hours of energy for a given size truck. The same considerations apply in railroad applications, and, to a lesser extent, to automotive applications. However, in automotive applications, the addition of calcium instead of antimony as the hardening agent for grids reduces the quantity of explosive gases generated and results in a battery which does not require maintenance, since the life is five years or less, and sufficient additional electrolyte is initially provided to allow for losses due to disassociation of the water. Obviously, this approach is not useful for batteries intended for industrial use or long life.
The instant invention overcomes these and other disadvantages and problems of the prior art.